Process for making urea-formaldehyde molding compositions and products therefrom



Patented Sept. 7, 1943 PROCESS FOR MAKING UREA-FORMALDE- HYDE MOLDINGCOMPOSITIONS AND PRODUCTS THEREFROM Leonard Smidth, Houston, Tex.

No Drawing. Application April 3, 1933,

Serial No. 664,207 I 7 Claims.

The invention is concernedwith the reaction products of urea orequivalent substances with formaldehyde or equivalent substances.

An object of my invention is to uniformly produce a superior hot moldingcomposition of increased plasticity or 'fiowf and rapid cure." Anotherobject is to quickly and uniformly produce a molding composition in anygiven coloror fiow" from a single condensation product.

A further object is to produce homogeneous molded products of increasedstrength andv durability and decreased brittleness by subjectin mymolding composition to the combined action of heat and pressure.

In preparing molding compositions from urea and formaldehyde whichquickly set when placed in a mold and subjected to the combined actionof heat and pressure, trouble is experienced because of the lack of flowof the- .composition will be increased when the composilution was 6.0.This was then mixed with 80 g.

of paper. The mixture was dried and pulverized.

When the above molding composition was placed in a given hot mold andsubjected to a given pressure without the addition of free urea.

it required thirty seconds to close the mold.

When 100 g, of the'said molding composition was thoroughly ground with 5g. of urea this composition was placed in the samemold'unde'r the sameconditions and it required only'eight seconds to close the mold.

The thiourea is preferable to urea because not only does it plasticizethe composition but also tion is subjected to the combined action ofheat and pressure in the mold,

' In practice, the thiourea or urea in its crystaled tothe moldedcomposition in its pulverized form. The molded composition with itsadded thiourea or urea. is then thoroughly mixed -to form a homogeneousmass before it is placed in line form is preferably pulverized and. thenaddthe mold. I have found that if the thiourea or urea is not thoroughlypulverized andmixed with the moldim compositionrthe molded product tendsto be sp0tty."

. The proportion of thiourea or urea to 'the molding composition mayvary within quite wide "limits but should be less than 10% (ten percent)by weight of the molding composition and should, preferably, bein excessof that which would react with the formaldehyde present in with 200 cc.of formaldehyde. The pH of the soit acts as an accelerating agent duringthe molding. It is ideal for this purpose because it does notappreciably increase the acidity of the composition, and thus thestability of the composirtion is not affected. During the hot moldingprocess sufficient ammonium thiocyanate is formed to greatly acceleratethe reaction. (When thiourea is heated it forms an equilibrium mixturewith ammonium thiocyanate.) It'is not desirable to add much morethiourea than 5% if an ordinary steel mold is used, because it will tendto stain the mold.

Another advantage is that a composition can be prepared from urea andformaldehyde containing less than the required proportion of urea toformaldehyde during the reaction and drying process such compositionbeing more stable because of the excess formaldehyde. (The optimumproportions, namely, between 1.05 to 1.40 moles of urea to 2 moles offormaldehyde are set forth in co-pending application Serial No.-

363,397.) Then the required amount of dry urea or thiourea is mixed withthe composition and the reaction goes to-completion during the mold-.ing process. For example, 1 mole of urea was retherewith, This gave astable molding compo- ,sition which readily flowed in. the hot mold andgave a molded'product resistant to weather.

One disadvantage of using dry urea or thiou- .rea is that unless it isthoroughly .mixed or ground with the composition it will tend to bespotty. If a pebblemill is used to grind in the thiourea or urea it willbe found that the composition 'becomes stiffer as the grinding proceeds,thus neutralizing the effect of the addition. Another disadvantage isthat since the flow of the different compositions vary and thus theamount of thiourea or urea added differ proportionately, the compositionwill vary in the ratio of urea to formaldehyde Accordingly, theinvention hereafter shown gives a method of overcoming both of the abovedisadvantages and is set forth in application Seria1 No. 514,544, filedJune 1, 1931.

Urea formaldehyde molding compositions containing paper as fillers whichare in use commercially, are described in my co-pending applicationSerial No. 363,397, filed May 15, 1929. These are made by reacting aurea with formaldehyde and then mixing or masticating the condensationproduct with paper. The material is then dried, usually with theapplication of heat. During the drying process, the composition ispartially converted to the final infusible, insoluble state. The nearerthe reaction is to completion, the greater is the resistance of thecomposition to flow. Different batches tend to vary in their flow evenwhen dried under the same conditions, due to variables which aredifficult, if not practically impossible to control. It is thisvariation ofthe batches which makes it diflicult to make vmoldingcompositions of ;uniform flow. Great caution has to be exercised toproduce a composition which will flow properly. If the material beforeit is pulverized is not sufliciently dry it will not pulverize readily.The pulverizing stage is normally reached while the material stillcontains moisture. At this stage the moisture may equal 5 to If thedrying is carried too far, the resultant material will not flow readilyenough. One method of accomplishing a uniform flow is to mix a largenumber of batches together, thus getting an average, but' this iscumbersome and not always satisfactory,

The principal object of this invention accordingly is to provide aprocess for manufacturing a superior urea-formaldehyde moldingcomposition which has a substantially uniform flow under heat andpressure and which yields products that have a high resistance toboiling water and other desirable characteristics as found in suchcommercial products.

I have found in accordance with this invention that a,urea-formaldehyde-molding composition of uniform flow can be obtainedsimply'by adding to such a molding composition a solution of a urea andformaldehyde or preferably their reaction products in order to make itas plastic as desired. In other words, I can heat my ureaformaldehyde.molding composition until I am certain it is dry and so that itpulverizes easily,

and regardless of how stiff (i. e., flow resistant) the composition hasbecome, I can make it any flow I wish, simply by the addition of theureapreciably affecting the molded product.

in 216 pounds of formaldehyde (pH 6.0) heated to 30 C. This was mixedwith 50, pounds of alpha fibre, .followed by drying to completion withheat and reduction to powder. This powder in a given mold required 30seconds for the closing. A solution made by heating 5 pounds of urea in10 pounds of 40% formalin (pH 3.0) to 50 C. was added and 8 seconds werenow required to close the same mold.

Example 2.100 pounds of urea were dissolved in 216 pounds offormaldehyde (pH 6.0) heated to 30 C. This was mixed with 50 pounds ofalpha fibre, followed by drying to completion with heat and reduction topowder. This powder in a given mold requires 30 seconds for-the closing.A solution made by heating 5 pounds of thiourea in 10 pounds of 40%formalin (pH 3.0) to 50 C. was added and 8 seconds were required toclose the same mold.

Example 1.--100 pounds of.urea were dissolved Example 3.Instead ofadding the solution of 5 pounds of urea in 10 pounds of formalin, as inExample 1, 15 pounds of solution made in the same way (1 part of urea in2 parts of 40% formalin) but 25% by weight of. water was removed undervacuum and the flow reduced in the same manner.

Example 4.'--Instead of adding the solution of urea in formalin, 5pounds of paraformaldehyde and 5 pounds'of urea were added to 5 poundsof triethanolamine. .If this is heated to cause solution and partialreaction, the resulting mixture can be used to increase plasticity ofurea-formaldehyde molding compositions.

Example 5. -5 pounds of urea and 5 pounds of paraformaldehyde were addedto 5 pounds of a 1 to 1 mixture of ethyl alcohol and water, and themixture heated. The resulting opaque fluid was then mixed withurea-formaldehyde molding compositions and its plasticity wasaccordingly increased.

The molding compositions made in accordance with the above examples-havea quick uniform flow and give excellent molded articles. The

.products possess the resistance to boiling water and othercharacteristics desired commercially.

Of course the dried molding composition may be prepared.with a molarproportion of urea less than desired in the final product. In such casethe "softening mixture should contain a sumcient excess of urea to makeup for the deficiency. The greater the proportion of formaldehydereacted with urea in the dried composition, the greater will be itsplasticity, while the greater proportion of urea in the liquid mixture,the greater will be the plasticity. A formaldehyde rich softening"mixture could be added to a molding composition containing an excess ofurea but usually is not-desired since the formaldehyde is in watersolution and the addition of any substantial quantity of aqueousformaldehyde would wet the powder too much. However, this can beovercome by using solid forms of formaldehyde, such as paraform orhexamethylene-tetramine dissolved in a small proportion of a mutualsolvent with urea.

Molded products prepared from urea-formaldehyde molding compositions arerelatively brit- I uble.

I soluble in the ureav formalin mixture, such as losolve and thissolutionslowly pouredinto the I have found that the reason thatsubstances which are the most desirable softeners cannot be used,,is dueto the water present (or formed during the molded process) the presenceof which.

cuts down the solubility of the plasticizer. I

have found that in order to mix the softener with a urea-formaldehydemoldingcomposition .prepared in ordinary way from urea. and formalin itis necessary that the water content of the mixture be kept very low. Ifthe urea-formaldehyde molding composition is heated in order to dry itand reduce the water content sufficiently low, and the softener added,the mixture will be found to be so stiif that it has little value as amolding composition. 4

Now I havefound that if I continue the drying of my urea-formaldehydemolding compositions (e. g., as prepared in my co-pending applicationSerial No. 363,397, filed May 15, 1929) until the water content is'verylow, I- can add my plasticizing mixture consisting of aurea-formaldehyde condensation product in the presence of a nonaqueoussolvent and a softener. The prepara-'- tion of a urea-formaldehydecondensation product in .liquid solution substantially free of water isrelatively expensive. and in the process, outlined above no more than ofthis expensive composition so prepared is more stable on standing thanone made directly from urea formalin or plasticized by one. Suchcomposition has better molding' characteristics, i. e'., the flow of thematerial when the mold is closed is more even. The final molded productcontaining the softener is less brittle. The fact that there is lesswater present makes the molded product less likely to blister on accountof less gas present during the liquid plasticizing mixture.

boiling paraform mixture. Boiling was continued until the solutionbecame viscous. The solution when cold was sticky and viscous, and wasnotentirely clear. When heated, it became mobile and less viscous anddid not show, any tendency'to gelatinizea If 2 pounds of triethanolaminewere mixed with the paraform Cellosolve. mixture, the final solutionobtained would be found clear and transparent. 5 pounds of dibutylphthalate was added to the mixture inwhich it was soluble. Theplasticizing mixture was then added to 100 pounds of a thoroughly driedurea-formaldehyde. molding composition prepared according to myaforementioned copending application Serial No. 363,397. The pH of adistilled water extract of the plasticized molding composition was 6.5.Before adding the plasticizing mixture the composition was so stifi'that it hardly flowed in the mold but after the addition it became veryplastic.

Many advantages arise from the use ofmy It is desirable to prepare themolding. composition in coarse or granular formSo that blanks may bereadily pre-.

densation product including a filler, pigment, lake water-free mixtureneed be used. I find-that the 4 present a higher temperature and thus ashorter time in the mold is required.

Several methods for preparing. liquid plasticizing mixtures free fromwater can be used in which the most of the common softeners are 501- l.Formaldehyde in solution'in organic solvent is reacted with urea.

2. Dry dimethylol urea. in an organic solvent is reacted withformaldehyde.

3. Urea and aqueous formaldehyde is. reacted and the water present istaken off by means of binary, ternary, etc. mixtures of organicsolvents. 1 I

4. Paraformaldehyde or solid polymers'of formaldehyde are reacted withurea, and either during or after reacting organic solvents are added.

Examples of'softeners which maybe used alone or mixed in accordance withthis invention are as follows: The diethyl or dibutyl estersof oxalic,tartaric, or phthalic acid, p-toluol sulphonamide resin, benzyl alcohol,bomeol, camphor, glycol or glyceryl esters, acetanilide, vinyl resins,cellulose esters and the like.

The following is an example of carrying out my invention:

5 pounds paraform was stirred with 2 pounds Cellosolve. There was notcomplete solution.

The mixture was then acidified with acetic acid so that a test made witha portion dissolved in distilled water gave a pH of approximately 5.

6 pounds of urea. were dissolved in 1 pound Celordye, and possibly amold lubricant, it is generally necessary to grind the mixture to a finepowder in a pebble mill. Now I have found that I can readily obtainagranular coarse molding composition from a mixture plasticized with myfluid condensate in several ways. One method I is to run the fine powderthrough warm (preferably not over 60 C.) or cold rolls whose surface iscovered by the liquid plasticizing mixture (preferably by spraying).This 'g' /es sheets or sections which may be ground to desired size.Another'method is to place the molding composition and-liquidplasticizing mixture in a suitable mill, mixer, or masticator. Eith'erheat is applied or else the mixture is stirred until the temperature israised by the heat of reaction until a cake is formed. After cooling andspontaneous or forced drying, the cake is then broken down .to therequired granule sizes. Still another method is to take the compositionwetted paratus.

with the liquid plasticizing mixture and force it through a sieve orscreen of a given size by means of a rubbing or rolling action. 7

Another feature of the above invention is that it is adapted to thecommercial production of a molding composition to match any color atwill.

Then compositions with differentflows would be desirable with differentmolds. For tall objects which are molded in a deep die, a very plasticmaterial is more suitable, whereas a flat die would require the use of astiffer composition. To prepare and dry each one of these variations asthey are required would be tedious and expensive, requiring the frequentcleaning of all ap To stock all colors would be impos sible. The factthat a great many compositions stiffen on standing adds to thedifficulties.

The above invention shows a way to first prepare and dry the uncoloredmolding composition which can be used as a basis for quickly preparingmolding compositions of practically any desired color or flow. A largestockof powdered dry uncolored material is kept on hand. When a specificcolor is desired the pigment, lake or dye is added to the uncoloredpowder and the whole thoroughly mixed. Then the plasticlzing mixture isadded to regulate the flow to that desired. Since during the mixing andgrinding process the composition will tend to set or stifien it is bestto add the plasticizing mixture after the mixing and grinding process.If a stifier material than that obtained after the grinding 2. Afree-flowing molding powder as recited in claim 1, inwhich the absorbedliquid is aqueous.

3. A free-flowing molding powder as recited in claim 1, in which theabsorbed liquid comprises an organic solvent.

4. A free-flowing molding powder comprising a powdered solidintermediate condensation product of a urea and formaldehyde containing-':a cellulose filler, the mole ratio of the urea thereis desired, thecomposition is kept in the mill until in being less than 1.40 moles ofurea to 2 moles the desired flow is obtained. of formaldehyde, thepowder containing not more Instead of urea, thiourea or substitutionprodthan by weight of an .absorbed liquid senets of urea or of thioureamay be used in so far lected from the group consisting of (a) a soluasthey are not specifically limited, all of which tion of a urea andformaldehyde, and (b) a so- I wish to be included along with urea in thedes- '15 lution of a urea-formaldehyde reaction product, ignation ureaused in the following claims. said liquid containing suflicient excessurea to The formaldehyde may be used either in the give a mole ratio ofurea to formaldehyde in the commercial aqueous solution or in thegaseous total mass of between 1.05 to 1.40 of urea to 2 of state or inthe form of a solution'of anhydrous I formaldehyde, said absorbed liquidimparting to formaldehyde or in the form of the polymers. I 20 themolding powder an increased plasticity in the Thus while I havedescribed my improvement mold under heat and pressure. in detail andwith respect to certain preferred 5. A free-flowing molding powdercomprising forms, I do not desire to be limited to such dea powderedsolid intermediate condensation tails or forms since, as will be noticedby those 7 product of a urea and formaldehyde containing skilled in theart, after understanding my ina cellulose filler, the mole ratio offormaldehyde vention many changes and modifications may be therein beingless than 2'moles of formaldehyde made and the invention embodied inwidely diffto 1.40 moles of urea, the powder containing not erent formswithout departing from the spirit more than 20% by weight of an absorbedliquid and scope thereof in its broader aspects, and I selected from thegroup consisting of (a) a soludesire to cover all modifications, formsand imtion of a urea and formaldehyde, and (b) a soluprovements comingwithin the scope of any one honor a urea-formaldehyde reaction product,or more of the appended claimssaid liquid containing sufficient excessformal- This application is a continuation in part of dehyde to give'amole ratio of urea to formaldeapplication Serial Nos. 422,544, filedJan. 22, 1930, hyde in the total mass of between 1.05 to 1.40 of nowPatent No. 2,209,943, dated July 30, 1940; urea to 2 of formaldehyde,said absorbed liquid 541,544 filed June 1, 1931. iimparting to themolding powder an increased Compositions comprising fusible reactionprodplasticity in the mold under heat and pressure. ucts of urea andformaldehyde and a latent cat- 6. A free-flowing molding powder asrecited alyst or accelerating agent and the process of in claim 1, inwhich they absorbed liquid conresinifying such products by heat andpressure 40 tains a. softening agent for'the solid condensaare notclaimed herein since such compositions tion product. l and process areclaimed in my co-pending U. S. '7. A process of making a free-flowingmolding application Serial No. 489,099, filed May 29, 1943. powdercomprising drying a solid urea-formal- Having thus described myinvention what I dehyde intermediate condensation product conclaim asnew and desire to secure by Letters Pat- 5 taining a-cellulose filleruntil the solid is readily entis: pulverizable, pulverizing said solidcondensation 1. A free-flowing molding powder comprising product to forma powder, and mixing said powa powdered solid intermediate condensationprodder with not more than 20% by weight of a liquct of a urea andformaldehyde containing a celuid selected from the group consisting of(a) a lulcse filler, the powder containing not more than so solution ofa urea and formaldehyde and (b) a 20% by weight of an absorbed liquidselected solution of a urea-formaldehyde reaction prodfrom the-groupconsisting of (a) a solution of not, the sum of the absorbed urea andformal- ,a urea and formaldehyde, and (b) a solution of dehyde in thetotal mass being in a mole ratio a ureaformaldehyde reaction product,the sum of between 1.05 to 1.40 of .urea to 2 of formalof the absorbedurea and formaldehyde in the y 581d ed l quid imparting to the totalmass being in a mole ratio of between 1.05 o d Powder an increasedplasticity in the to 1.40 of urea to 2 of formaldehyde, said abmoldunder heatand Pressure. sorbed liquid imparting to the molding powder van increased plasticity in the mold under heat I LEONARD SMIDTH. andpressure. m

CERTIFI GATE OF CORBECTI ON Patent No. 2,529,172 September 7, 1919.

I LEONARD SMIDTH.

It is hereby certified that error appears in the printed specificationiring correction as follows: Page 5, secd--5.5--; and that the saidLetters Patrein that the same may conform of the above numbered patentrequ 0nd column, line 18, for "6.5" rea ent should be read with thiscorrection the to the record of the case in the Patent Office.

Signed and sealed this 25rd day of November, A. D. 1915.

Henry Van Arsdale;

(Seal) Acting Commissioner of Patents.

